Syrian forces backed by Russian warplanes continued to pound the Damascus suburb with at least 27 killed on Wednesday, bringing the civilian death toll to more than 270 – including 60 children – over the past three days.

“My appeal to all those involved is for an immediate suspension of all war activities in Eastern Ghouta,” Guterres told a UN Security Council meeting. “This is a human tragedy that is unfolding in front of our eyes, and I don’t think we can let things go on happening in this horrendous way.”

About 400,000 people live in the area, which has been besieged for years by government forces with few supplies reaching the desperate population.

UN human rights chief Zeid Ra’ad al-Hussein called the air strikes and artillery fire a “monstrous campaign of annihilation”.

“International humanitarian law was developed precisely to stop this type of situation, where civilians are slaughtered in droves in order to fulfill political or military objectives,” he said in a statement.

The UN has documented 346 civilian deaths with 878 wounded in Eastern Ghouta since February 4, mostly from air strikes hitting residential areas, Zeid said.